Liposomes are closed vesicles comprising a lipid bilayer. Taking advantage of bioaffinity of liposomes, a number of proposals have been made to incorporate various drugs into the inner aqueous phase or the lipid bilayer of liposomes for use as a drug carrier. In many cases, however, liposomes as suspended in water are colloid-chemically instable, tending to undergo agglomeration or fusion among themselves, precipitation due to crystallization of the membrane component, an increase in particle size, or hydrolysis to form lyso-phospholipids that are considered to be hemolytic. These changes in effect and appearance result in impairment of commercial values.
Unexamined Published Japanese Patent Application No. 42733/87 furnishes a solution for the problem, which comprises stabilizing liposomes using an amino acid. What is achieved by this technique is stabilization in preservation at room temperature or lower temperatures, and stabilization in high temperature preservation was still insufficient. The technique was also insufficient for inhibition of lyso-phospholipid formation.
An object of the present invention is to provide a stable liposome aqueous suspension which does not undergo precipitation, agglomeration or change in particle size even when preserved at 40.degree. C. for 6 months and in which lyso-phospholipid formation is suppressed.